1. Field of the Invention
The present invention relates to a barrier mechanism incorporated into a lens barrel of, for example, a digital camera, a silver-halide camera, or a video camera.
2. Description of the Related Art
In a high-magnification zoom lens barrel with a barrier mechanism, a first lens unit has a convex lens through which the interior of a second lens unit is magnified and thus dust coming into the zoom lens barrel is magnified. Therefore, a view will be deteriorated even with dust that is not visible, resulting in a demand for a more strict dust entrance prevention function.
Such a conventional barrier mechanism is known that includes barrier blades which rotate to open/close in front of a lens and a barrier drive member for driving the barrier blades (Japanese Patent Application Laid-Open No. 2004-258120).
The barrier mechanism controls the movement of the barrier drive member in an optical axis direction by using a partition which divides the barrier blades and the barrier drive member in the optical axis direction. Then, as a barrel moves in the optical axis direction, a rotational member such as a cam ring or the like, or a fixed cam allows the barrier drive member to rotate, thereby allowing the barrier blades to rotate (open/close) over the partition.
Recently, in order to reduce the number of apparatus parts, the barrier drive member is directly incorporated into the barrel using a bayonet structure to control the movement thereof in the optical axis direction, thereby allowing the barrier blades to rotate over the barrier drive member.
FIGS. 19 through 21 illustrate a conventional first lens unit barrel having the bayonet structure.
FIG. 19 is a view of the first lens unit barrel from an imaging surface side before a barrier drive member is incorporated into the first lens unit barrel. FIG. 20 is a view of the first lens unit barrel from the imaging surface side after the barrier drive member is incorporated into the first lens unit barrel and FIG. 21 is a view of the first lens unit barrel with the barrier drive member from an object side.
As shown in FIGS. 19 through 21, the first lens unit barrel 101 includes bayonet claws 101d into which flange portions 113d of a barrier drive member 113 fit, and a plurality of bayonet claws 101i and 101j which fit into a barrier cover (not shown) in a circumferential direction. An imaging surface side of the bayonet claws 101d, 101i, and 101j is provided with a hole 101l. 
The imaging surface side of the first lens unit barrel 101 is provided with shaft holes 101h which serve as rotational fulcrums of the barrier blades (not shown) and a through-hole 101f to rotationally move an interlocking lever 113f of the barrier drive member 113 within the first lens unit barrel 101 in association with a cam ring or the like.
A technique is discussed in Japanese Patent Application Laid-Open No. 2005-258276 that discharges moisture coming into the barrel due to an air flow while the barrel is retracted, through holes formed in a barrier of the barrel and closes the holes with a water repellant sheet.
In the above described technique, the barrier blades are positioned at an object side of the first lens unit barrel 101, and the cam ring and the fixed cam which rotate the barrier drive member 113 are positioned at an imaging side of the first lens unit barrel 101. Therefore, the barrier drive member 113 is required to convey a driving force through the first lens unit barrel 101, and therefore, as described above, the first lens unit barrel 101 needs the through-hole 101f for the interlocking lever 113f. 
In this case, if the barrier drive member 113 is to be attached to the first lens unit barrel 101 through the bayonet structure, it is required to provide the through-hole 101f in a wide angled range including an attachment phase of the bayonet claws 101d, 101i, and 101j. The through-hole 101f cannot be sealed with the water repellant sheet or the like in its entirety in the barrel as discussed in the Japanese Patent Application Laid-Open No. 2005-258276, and partial sealing of the through-hole 101f may cause a problem in rotating the barrier drive member 113.
In a molded barrel, if it is molded so that an undercut is omitted, a hole which allows a portion of a die to project from a parting line surface in the form of a convex shape is made. This is because the convex shaped portion can come into the opposite mold die. As a result, dust such as sand or dirt can easily enter the barrel through the hole or the through-hole 101f. 
Once the dust such as the sand or the dirt enters the barrel through openings of the barrier mechanism, the dust causes malfunction. Further, if the dust enters the barrel, the sand or the dirt becomes visible through the first lens unit. In particular, in the case where the first lens unit is a convex lens, deterioration of the view occurs since the dust such as the sand or the dirt is magnified.